If it is necessary to put nail polish on because of some medical problems, there is a concession allowing it and it should be wiped over when doing wudu or ghusl.

The majority of scholars are of the view that wudu is an essential condition of tawaf. However, wudu is not essential for sa`i.

Before wudu, you should say Bismillah. After wudu, you can say this du`a, “Ashhadu an la ilaha ill-allah wahdahu la sharika lah, wa ashhadu anna Muhammadan ‘abduhu wa rasuluhu.” For more, see the detailed answer.